The invention relates to a thermally stabilized polymeric composition which exhibits improved thermal stability, a method of improving the thermal stability of polymeric composition, and an electrical conductor coated with, a cable jacketed with and heat recoverable article made from the stabilized polymeric composition.
Polyesters, such as poly(alkylene terephthalates), for example, poly(ethylene terephthalate) (PET) and poly(butylene terephthalate) (PBT), are subject to thermal degradation, especially at elevated temperatures. It is known, generally, to modify such polyester compositions containing 0 to 60 weight percent of fillers with a polymeric modifier such as polycaprolactone (PCL) but the degree of thermal stabilization provided in this manner is not sufficient for many uses.
U.S. Pat. No. 3,835,089, to Fox and Wambach, recognizes that the physical properties of blends of PBT and PCL are improved over those obtainable with the individual components. This patent does not, however, recognize that PBT/PCL blends can be still further improved with respect to thermal aging properties.
European patent application EP 57, 415 A2 of Ogawa and Akagi discloses compositions of polyester and a modified polycaprolactone. The compositions can further contain various additives such as inorganic fillers, e.g., glass fibers, crystal nucleating agents, phosphorus compounds, epoxy compounds, and other additives, such as flame retardants, antioxidants and heat stabilizers. The addition of phosphorus compounds is said to enhance the heat resistance of the composition. Examples of phosphorus compounds given in this European application include phosphates, phosphites, phosphonic and phosphinic compounds. Trimethyl phosphate and triphenyl phosphite are listed as examples of preferred phosphorus compounds. We have found that phosphates and aryl phosphites are not effective in enhancing the thermal stability of blends of poly(butylene terephthalate) and poly(caprolactone).
The compositions described in the above documents do not possess the degree of thermal stabilization sufficient for many uses.